Variable-Rate Techniques Not Ready for Manure Application

Manure application equipment just isn’t accurate enough for efficient nutrient application, according to a recent Manitoba study. The $54,750 study, jointly funded by the Manitoba Rural Adaptation Council (MRAC), the Manitoba Pork Council and producer participants, was carried out by Agra-Gold Consulting and Farmer’s Edge Precision Consulting.

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Manure application equipment just isn’t accurate enough for efficient nutrient application, according to a recent Manitoba study. The $54,750 study, jointly funded by the Manitoba Rural Adaptation Council (MRAC), the Manitoba Pork Council and producer participants, was carried out by Agra-Gold Consulting and Farmer’s Edge Precision Consulting.

The study involved 13 producers, each of whom provided about two quarters of land, a sampling base which represented a cross-section of Manitoba cropping conditions. Manure was applied using the drag hose application method.

Tractor operators varied application rates according to GPS field maps indicating differing nutrient requirements in different parts of the fields. The zones were determined using satellite imagery, which uses different light bands to create an NDVI (vegetative index of better growing parts of the field). These zones were then individually soil tested to determine the reasons for the variability across zones and to determine the optimal nutrient application rate.

Project leader Scott Dick says a growing number of producers are using variable-rate application with commercial fertilizer to tailor application rates to the varying nutrient requirements on different parts of a field. The result can lead to better nutrient utilization by the crop, higher yields, lower costs, and reduced environmental risk of excess nutrients contaminating water supplies.

Adapting variable-rate techniques to manure application appears to have good potential, Dick says, but additional refinement is needed in applicator technology. “Producers accepted the methodology used in creating the different management zones, but they weren’t ready to embrace this precision approach yet,” he reports.

Researchers found the commercial drag-line equipment used to apply manure couldn’t accurately and efficiently vary application rates to match specific nutrient needs, according to Dick. Equipment operators could only adjust application rates by speeding up or slowing down the tractor speed. “On a half-mile run, that could mean between one and three speed adjustments – not a major problem, but enough to affect accuracy,” he says.

In addition, without an on-the-go sensor to determine soil nutrient levels, planners had to rely on past soil analyses to determine application rates. “The only way to accurately measure nutrient levels was to send a sample to the lab after application,” Dick explains.

While the study indicates variable-rate manure application is not commercially feasible now, it outlines ways producers can use precision farming techniques to increase yields and reduce environmental risks. Producers can, for example, begin by applying a base rate of manure using conventional techniques, then follow up with a variable-rate application of commercial starter fertilizer at seeding time. This approach gives producers time to get accurate manure and soil analyses results back from the lab to accurately match nutrient applications with crop requirements.